The present invention relates to an electronic spark timing advancing apparatus of an internal combustion engine, and more particularly to an electronic spark timing advancing apparatus which provides an optimum spark timing advancement characteristic to the engine.
A prior art electronic spark timing advancing apparatus has been constructed to provide an optimum spark timing with respect to fuel consumption, exhaust gas and torque in accordance with an input signals such as rotation speed of the engine, manifold vacuum, temperature of cooling water or the like. Such a prior art apparatus, however, requires a complex function generator for determining an optimum spark timing in accordance with the input signals. Thus, when a sophisticated control is desired, the apparatus would be very expensive. Furthermore, because the apparatus does not function as a system to sense combustion state of the engine, a spark timing for an optimum combustion condition must be previously calculated. This requires considerable manpower and cost.
The Japanese Patent Application Kokai No. 50-153137 and Japanese Patent Application Kokoku No. 46-3525 disclose electronic spark timing advancing apparatus in which an internal pressure of a cylinder is sensed and an optimum crank angle at which the internal pressure of the cylinder is to assume a peak value under a normal operation is determined from a viewpoint that fuel consumption, exhaust gas and torque are maintained under best conditions in the normal operation, and a differential angle between the actual peak angle and the optimum peak angle of the internal pressure is fed back to control the spark timing so that the actual internal pressure assumes the peak value at the optimum crank angle. In this apparatus, the drawbacks described above have been overcome and the peak angle of the internal pressure is controlled to assure the optimum conditions of the fuel consumption, torque and exhaust gas under the normal operation. However, it had a drawback that much noxious exhaust gas is ejected under certain conditions such as rapid acceleration of the engine, warming-up of the engine or engine braking.